1. Field
Embodiments relate to a semiconductor device.
2. Description of the Related Art
When growing a thin film on a primary surface of a substrate, in particular, a semiconductor substrate to form a semiconductor device, the primary surface of the semiconductor substrate is exposed to source gas for forming the thin film while the semiconductor substrate is heated. The source gas may contain, for example, an organic metal compound of a Group III nitride semiconductor as a cation or may contain a Group V element as an anion. By supplying the source gas onto the primary surface of the semiconductor substrate, the thin film is grown on the primary surface of the semiconductor substrate.
The above-mentioned method of growing the thin film is called a vapor phase growth method. Vapor phase growth method is one form epitaxial crystal growth. When growing a thin film on a substrate using the vapor phase growth method, for example, a material of the thin film may be different from that of the substrate. The method of growing the thin film made of a material different from that of the substrate on the substrate is called a hetero epitaxial growth method. Moreover, the thin film formed using the hetero epitaxial growth method is called a hetero epitaxial film, and an interface between the hetero epitaxial film and the substrate is called a hetero interface. As will be described later, the substrate refers to a member on which a target thin film is formed, and the substrate may comprise a single-layered substrate on a primary surface of which the target thin film is formed, and a substrate comprising one or more thin films previously formed thereon (a substrate on which an epitaxial film is previously formed and is defined as an epi-wafer). In the latter case, the target thin film is formed on the previously-formed thin film on the substrate.
When forming the above mentioned hetero epitaxial film, for example, an InGaN thin film grown on a group III nitride semiconductor film such as a GaN crystal film may be problematic in that it is difficult to achieve a sharp gradient of an indium (In) concentration change near an interface between the InGaN film and the GaN film.
To be specific, the InGaN thin film having a desired indium concentration may not be formed on the GaN film. For example, when forming the InGaN thin film having a thickness of approximately 5 nm, a transition layer having a lower indium (In) concentration may be formed up to approximately 1 to 2 nm in a direction of the thickness of the InGaN film from the interface between the InGaN and GaN films. Such a transition layer may prevent the indium concentration change nearby the interface between the InGaN film and GaN film from having a sharp gradient. This phenomenon may also occur when growing an AlGaN thin film on the GaN crystal film in the hetero epitaxial growth manner.
The transition layer having such a lower or non-uniform indium concentration, formed near the interface using the hetero epitaxial growth method, may deteriorate characteristics of the semiconductor device employing the hetero epitaxial film. Therefore, in order to improve the characteristics of the semiconductor device employing the hetero epitaxial film, it is necessary to suppress the transition layer so that the sharp gradient of the concentration of the thin film near the hetero interface is achieved when using the hetero epitaxial growth method.